With the intention of identifying novel genes involved in the arterial response to injury we undertook a differential screen of genes expressed in normal and injured arteries. We identified a novel sequence that with the exception of bone was not expressed in normal tissues, but highly induced in injured arteries. This cDNA contained an open reading frame of 245 amino acids with no significant homology to any known protein with the exception of a 36 amino acid (aa) long domain with 59% homology to the helical repeat regions found in collagens. Comparison with the human cDNA revealed 98% identity at the amino acid level indicative of a highly conserved protein. Northern blotting of mRNA derived from various adult rat organs revealed significant levels of this mRNA only in bone and lung. In balloon-injured arteries expression of this mRNA was prominent in adventitial fibroblasts during the proliferative and remodeling phase and only little expression was seen in smooth muscle cells of the developing neointima. Bone showed expression in the matrix of resting, proliferating and hypertrophic chondrocytes but expression was lost from the matrix as chondrocytes reached the apoptotic zone of the growth plate. Expression was also observed in periosteal cells. Based on its expression pattern, we named the gene remodelin. Several findings indicate that remode!in has important biological functions particularly in the arterial response to injury as well as in bone and cartilage matrix formation. These include: 1) increased remodulin expression in vitro is associated with decreased TGF-Beta expression as well as reduced TGF-Beta dependent gene expression (collagens type I and III), 2) increased remodulin expression in vivo results in phenotypes reminiscent of collagen mutants found in osteogenesis imperlecta (01), dystrophic epidermolysis bultosa (DEB) and myopathies (Bethlem), 3) in the absence of remodelin, expression of bone differentiation markers such as osteopontin and alkaline phosphatase (ALP) are dramatically increased, and 4) inhibition of Cbfa1 dependent gene expression such as osteocalcin by remodeiin. As such, remodelin appears to be an in vivo regulator of skeletal tissues and wound healing responses, potentially influencing calcification and differentiation along the chondrocyte/osteoblast lineages. As a potential inhibitor of calcification in the vessel wall this proposal will examine the role of remodelin in vascular calcification and remodeling using both in vitro and in vivo approaches.